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CDKN2A gene deletions and loss of p16 expression occur in osteosarcomas that lack RB alterations
G P Nielsen1, K L Burns, A E Rosenberg
1James Homer Wright Pathology Laboratories, Department of Pathology and Neurosurgical Service, Massachusetts General Hospital and Harvard Medical School, Boston 02114, USA. gnielsen@partners.org
Abstract:
Osteosarcomas often suffer mutations of the RB (retinoblastoma) gene, with resultant inactivation of the pRb protein. pRb is one component in a cell-cycle control pathway that includes the p16 (encoded by the CDKN2A gene) and cyclin-dependent kinase 4 (cdk4, encoded by the CDK4 gene) proteins. We therefore sought to determine whether the CDKN2A and CDK4 genes were altered in those osteosarcomas that lacked RB inactivation. Twenty-one osteosarcomas (2 low-grade and 19 high-grade) were evaluated for homozygous deletion of the CDKN2A gene, CDK4 amplification, and allelic loss of the RB gene, as well as for expression of p16 and pRb proteins. Five high-grade osteosarcomas showed loss of p16 expression; four of these had homozygous CDKN2A deletions, and the fifth had a probable deletion obscured by numerous nonneoplastic, p16-immunopositive multinucleated giant cells. Thus, p16 immunohistochemistry may provide a sensitive means for assessing CDKN2A status. Twelve tumors (including the two low-grade osteosarcomas) were immunopositive for pRb, and nine tumors were immunonegative for pRb. Of the five cases with CDKN2A/p16 alterations, none had allelic loss of the RB gene and all expressed pRb, suggesting that each of these tumors had an intact RB gene. None of the tumors showed CDK4 amplification. No alterations were detected in the two low-grade osteosarcomas. This study suggests that CDKN2A is a tumor suppressor inactivated in osteosarcomas that lack RB mutations and that the p16-pRb cell-cycle control pathway is deregulated in a large number of high-grade osteosarcomas.
Insights
Mutations in the CDKN2A gene, affecting p16 protein, are found in osteosarcomas lacking RB gene alterations. This suggests the p16-pRb pathway is frequently disrupted in high-grade osteosarcomas.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Osteosarcomas frequently exhibit mutations in the retinoblastoma (RB) gene, leading to pRb protein inactivation.
- The pRb protein is a key component of the cell-cycle control pathway, involving p16 and cyclin-dependent kinase 4 (cdk4).
Purpose of the Study:
- To investigate alterations in the CDKN2A and CDK4 genes in osteosarcomas that do not have RB gene inactivation.
- To understand the role of the p16-pRb cell-cycle control pathway in osteosarcoma development.
Main Methods:
- Evaluation of 21 osteosarcomas (2 low-grade, 19 high-grade) for homozygous deletion of CDKN2A, CDK4 amplification, and RB allelic loss.
- Assessment of p16 and pRb protein expression using immunohistochemistry.
Main Results:
- Five high-grade osteosarcomas displayed loss of p16 expression, with four showing homozygous CDKN2A deletions.
- No tumors exhibited CDK4 amplification. All cases with CDKN2A/p16 alterations retained an intact RB gene and expressed pRb.
- No genetic alterations were identified in the two low-grade osteosarcomas.
Conclusions:
- The CDKN2A gene is a tumor suppressor frequently inactivated in osteosarcomas lacking RB mutations.
- The p16-pRb cell-cycle control pathway is deregulated in a significant proportion of high-grade osteosarcomas.